Five Photons
Remarkable Journeys of Light Across Space and TimeJames Geach

The story of the Universe is written in the light that travels through it – light that we can capture. Nearly everything we know about how the Universe works on its grandest scale comes from the analysis of the light – photons – that may have travelled nearly fourteen billion years from the Big Bang itself to reach us.

Have you ever wondered what is the most distant source of light we can see, or how a star shines? Did you know that black holes can blaze like cosmic beacons across intergalactic space, and that ancient radio waves might herald the ignition of the very first stars? Have you ever thought about what light really is?

Five Photons explains all with the tales of five fascinating astrophysical processes through the journeys of light across space and time. They are tales of quantum physics and general relativity, stars and black holes, dark matter and dark energy. Let yourself be swept away on a journey of discovery towards a deeper understanding of the Universe.

‘Light illuminates cosmic origins and decodes quotidian realities. But what is it? This deft primer by astrophysicist James Geach captures the elusive electromagnetic wave in five processes. His meditation on ‘old’ light takes us back to the singularity: the “cosmic seed” that expanded into the Big Bang. A study of starlight plunges us into the seething stellar surface. We peruse dark energy, radio waves and quasars – beacon-like galaxies in which supermassive black holes feed off interstellar gas and release vast amounts of energy. A masterclass in elucidating hard science with elegance and brevity.’ – Nature

‘What makes Five Photons different . . . is the depth that Geach goes to – not in a mathematical sense, but in describing subtleties of the work of astrophysicists and cosmologists that popular science titles usually gloss over . . . Think of it as a sequel to A Brief History of Time that explains some of the real detail of what has been discovered and brings in factors cosmologists have to consider that you won’t see anywhere else in a popular science title.’ – Popular Science

‘Light permeates almost everything around us. It is the primary way in which we communicate and with which we try to understand the Universe. Light is the central theme of James Geach’s book. After an introductory chapter on what light is, the book identifies five different sources of light that are key probes of the cosmos. This framework allows Geach to cover everything from the cosmic microwave background, to stars, dark energy, black holes and the epoch of reionization. No equations are to be seen and the style is conversational, making this book a perfect entryway to anyone interested in learning a bit more about the inner workings of the Universe.’ – Nature Astronomy

‘In Five Photons, astrophysicist James Geach serves as our guide on this cosmic voyage. Geach explains five tales of fascinating astrophysical processes that propel light across space and time, tales of quantum physics and general relativity, stars and black holes, dark matter and dark energy. Sweeping us away on electromagnetic waves, Five Photons is a journey of discovery toward a deeper, more enlightened understanding of this breathtaking universe.’ – Fahrenheit, Pop Science Book Club

‘With his elegant, supremely clear writing, Geach has succeeded at creating both a state-of-the-art cosmic overview and a rather wonderful meditation on the nature of our reality.’ – Caleb Scharf, author of The Zoomable Universe

‘Geach’s beautiful cosmic biography takes readers on a sweeping tour of all that was, is, and ever will be. Five Photons is as elegant as it is enlightening.’ – Lee Billings, author of Five Billion Years of Solitude

‘Light illuminates cosmic origins and decodes quotidian realities. But what is it? This deft primer by astrophysicist James Geach captures the elusive electromagnetic wave in five processes. His meditation on ‘old’ light takes us back to the singularity: the “cosmic seed” that expanded into the Big Bang. A study of starlight plunges us into the seething stellar surface. We peruse dark energy, radio waves and quasars – beacon-like galaxies in which supermassive black holes feed off interstellar gas and release vast amounts of energy. A masterclass in elucidating hard science with elegance and brevity.’ – Nature

‘What makes Five Photons different . . . is the depth that Geach goes to – not in a mathematical sense, but in describing subtleties of the work of astrophysicists and cosmologists that popular science titles usually gloss over . . . Think of it as a sequel to A Brief History of Time that explains some of the real detail of what has been discovered and brings in factors cosmologists have to consider that you won’t see anywhere else in a popular science title.’ – Popular Science

‘Light permeates almost everything around us. It is the primary way in which we communicate and with which we try to understand the Universe. Light is the central theme of James Geach’s book. After an introductory chapter on what light is, the book identifies five different sources of light that are key probes of the cosmos. This framework allows Geach to cover everything from the cosmic microwave background, to stars, dark energy, black holes and the epoch of reionization. No equations are to be seen and the style is conversational, making this book a perfect entryway to anyone interested in learning a bit more about the inner workings of the Universe.’ – Nature Astronomy

‘In Five Photons, astrophysicist James Geach serves as our guide on this cosmic voyage. Geach explains five tales of fascinating astrophysical processes that propel light across space and time, tales of quantum physics and general relativity, stars and black holes, dark matter and dark energy. Sweeping us away on electromagnetic waves, Five Photons is a journey of discovery toward a deeper, more enlightened understanding of this breathtaking universe.’ – Fahrenheit, Pop Science Book Club

‘With his elegant, supremely clear writing, Geach has succeeded at creating both a state-of-the-art cosmic overview and a rather wonderful meditation on the nature of our reality.’ – Caleb Scharf, author of The Zoomable Universe

‘Geach’s beautiful cosmic biography takes readers on a sweeping tour of all that was, is, and ever will be. Five Photons is as elegant as it is enlightening.’ – Lee Billings, author of Five Billion Years of Solitude

James Geach is a Royal Society University Research Fellow and Reader in Astrophysics at the Centre for Astrophysics Research at the University of Hertfordshire, specializing in observational cosmology and the formation and evolution of galaxies. He is the author of Galaxy: Mapping The Cosmos (Reaktion, 2014).